Militant video claims deadly Syria bombings

Syrian soldiers check a burned truck in front of a damaged military intelligence building where two bombs exploded, at Qazaz neighborhood in Damascus, Syria, on Thursday May 10, 2012. Two strong explosions ripped through the Syrian capital Thursday, killing or wounding dozens of people and leaving scenes of carnage in the streets in an assault against a center of government power. (AP Photo/Bassem Tellawi)
— AP

Syrian soldiers check a burned truck in front of a damaged military intelligence building where two bombs exploded, at Qazaz neighborhood in Damascus, Syria, on Thursday May 10, 2012. Two strong explosions ripped through the Syrian capital Thursday, killing or wounding dozens of people and leaving scenes of carnage in the streets in an assault against a center of government power. (AP Photo/Bassem Tellawi)
/ AP

Syrians chant slogans during a demonstration at al-Hamra neighborhood in Homs, Syria, Friday, May 11, 2012. A Syrian opposition leader said Friday the regime is trying to destroy a U.N.-brokered peace plan for the country. (AP Photo)— AP

Syrians chant slogans during a demonstration at al-Hamra neighborhood in Homs, Syria, Friday, May 11, 2012. A Syrian opposition leader said Friday the regime is trying to destroy a U.N.-brokered peace plan for the country. (AP Photo)
/ AP

In this photo released by the Syrian official news agency SANA, a Syria man, right reacts as flames and smoke rise from burned cars after two bombs exploded, at Qazaz neighborhood in Damascus, Syria, on Thursday May 10, 2012. Two strong explosions ripped through the Syrian capital Thursday, killing or wounding dozens of people and leaving scenes of carnage in the streets in an assault against a center of government power. (AP Photo/SANA)— AP

In this photo released by the Syrian official news agency SANA, a Syria man, right reacts as flames and smoke rise from burned cars after two bombs exploded, at Qazaz neighborhood in Damascus, Syria, on Thursday May 10, 2012. Two strong explosions ripped through the Syrian capital Thursday, killing or wounding dozens of people and leaving scenes of carnage in the streets in an assault against a center of government power. (AP Photo/SANA)
/ AP

In this photo released by the Syrian official news agency SANA, men run between dead and injured people at the scene where two bombs exploded in the Qazaz neighborhood in Damascus, Syria, Thursday, May 10, 2012. Two large explosions ripped through the Syrian capital Thursday, heavily damaging a military intelligence building and leaving blood and human remains in the streets. (AP Photo/SANA)— AP

In this photo released by the Syrian official news agency SANA, men run between dead and injured people at the scene where two bombs exploded in the Qazaz neighborhood in Damascus, Syria, Thursday, May 10, 2012. Two large explosions ripped through the Syrian capital Thursday, heavily damaging a military intelligence building and leaving blood and human remains in the streets. (AP Photo/SANA)
/ AP

BEIRUT 
A video posted online in the name of a shadowy militant group late Friday claimed responsibility for twin suicide bombings in the Syrian capital this week that killed 55 people.

In the video, a group calling itself the Al-Nusra Front says the bombing was in response to attacks on residential areas by the regime of President Bashar Assad.

"We fulfilled our promise to respond with strikes and explosions," a distorted voice says, reading black text that rolls across a white screen while Islamic chanting plays in the background.

The Al-Nusra Front has claimed past attacks through statements posted on militant websites. Little is known about the group, although Western intelligence officials say it could be a front for an al-Qaida branch operating in Iraq. The video's authenticity could not be independently verified.

Western officials say there is little doubt that Islamist extremists, some associated with al-Qaida, have made inroads in Syria as instability has spread since the start of the uprising against President Bashar Assad 14 months ago.

But much remains unclear about their numbers, influence and activities inside Syria.

Their presence adds a wild card element to the Syria conflict that could further hamper international efforts to end it.

World powers are backing a peace plan presented by international envoy Kofi Annan that calls for a cease-fire to allow for talks on a political solution to the conflict.

A shipment of supplies for U.N. observers monitoring the truce arrived in Damascus Sunday. It included six armored cars, the first of 25 to arrive Saturday for use by the 105 military observers and 45 support staff currently in the country.

But while foreign diplomats and observers can pressure the government and the opposition to stick the plan, they have no means of influencing shadowy Islamic militants.

Friday's video said the Damascus attack was in response to Syrian government attacks on residential areas.

"We promised the regime in our last declaration to respond to its killing of families, women, children and old men in a number of Syrian provinces, and here we kept our promise," it says.

The video, which says it was made on May 10, the day of the Damascus bombings, also strikes a sectarian tone, calling for the protection of Sunni Muslims and threatening revenge against Alawites, the Shiite offshoot to which Assad and many members of his security services belong.

"We tell this regime: Stop your massacres against the Sunni people. If not, you will bear the sin of the Alawites. What is coming will be more calamitous, God willing," it says. It also advises Sunnis to avoid security offices - a veiled threat of future bombings.

Thursday's twin blasts in Damascus were the fifth in a string of major attacks in Syrian cities that have clouded the picture of a fight between the opposition and the regime. It was the deadliest yet, in part because it happened on a key thoroughfare during rush hour, while previous bombings were on weekends.

Syria's uprising started in March 2011 with mostly peaceful protests inspired by successful revolts elsewhere calling for political reform. The Syrian government responded with a brutal crackdown, prompting many in the opposition to take up arms to defend themselves and attack government troops.